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Chapter 7: Computation of the Reflection Coefficient on the Inlet air circuit of an Helicopter combustor 122 chamber Intake p ′ =0 BP Compressor HP Compressor T out = 584.6K P out = 894320Pa M out =0.05 Combus'on Chamber Figure 7.1: Air-intake duct configuration characterize the mean flow. 1 0.8 0.6 0.4 0.2 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Curvilinear Axis (m) Figure 7.2: Adimensional section area of the aeroengine air-intake duct Figure (7.3) show the mean field of total pressure and total temperature computed by SNozzle. In real engines, this pressure jump is not performed isentropically. As a consequence the evaluation of a polytropic coefficient η p is essential. ( ) γηp /(γ−1) ¯p t2 ¯T t2 = ¯p t1 ¯T t1 (7.1)
7.3 Acoustic Evaluation 123 In the present helicopter system, this coefficient is close to η p = 0.87 for the first compressor stage and η p = 0.9 for the second one. The mean field can be, as a result, be modeled properly in the computational analysis. This is shown in Fig. 7.3. 12 10 8 SNozzle Helicopter Engine Data 2.5 2 SNozzle Helicopter Engine Data 6 1.5 4 2 1 0 0 0.2 0.4 0.6 0.8 Curvilinear Axis (m) 0.5 0 0.2 0.4 0.6 0.8 Curvilinear Axis (m) a) Normalized Total Pressure b) Normalized Total Temperature Figure 7.3: Total Pressure and Total Temperature profiles 7.3 Acoustic Evaluation The reflection coefficient R = w + 2 /w− 2 is computed for the outlet section of the intake duct which corresponds to the inlet of the helicopter combustion chamber. It is evaluated for two different cases: • CASE A → Airline with total pressure jump: The evaluation of acoustics is done for the geometry including the compressors. It means that a total pressure jump is imposed to the mean flow. • CASE B → Airline without total pressure jump: In order to assess the actual influence of the compressors on the acoustics of the system, the acoustic response of the intake is done without any total pressure jump. In fact, this is how the reflection coefficient was used to be computed [41] before the development of the Snozzle tool. It is noticeable that the presence of the compressors increases the amplitude of the reflected wave (Fig. 7.4 a). When no total pressure jump is imposed, the amplitude of the reflected wave is similar to the forced one, whereas it is twice as large when the work done by the compressor is accounted for. The phase of R (Fig. 7.4 b) also changes when the compressors are added to the system.
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UNIVERSITE MONTPELLIER II SCIENCES
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An expert is a man who has made all
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Y gracias familia mía!!, que así
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Abstract Today, much of the current
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4 CONTENTS 3.4.1 Preconditioning .
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List of Figures 1.1 Main sources of
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8 LIST OF FIGURES 5.19 Acoustic ene
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List of Tables 1.1 EU recommended r
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14 Chapter 1: General Introduction
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2 Computation of noise generated by
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22 Chapter 2: Computation of noise
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42 Chapter 3: Development of a nume
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4 Validation of the acoustic code A
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60 Chapter 4: Validation of the aco
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Page 138 and 139: Bibliography [1] AGARWAL, A., MORRI
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